feat: ✨ handle reserver identifiers (#8)

src/cst-definitions.d.ts

@@ -53,6 +53,7 @@ export interface AtomicExpressionCstNode extends CstNode {
 export type AtomicExpressionCstChildren = {
   Integer?: IToken[];
   identifier?: IdentifierCstNode[];
+  ReservedIdentifiers?: IToken[];
 };
 
 export interface ICstNodeVisitor<IN, OUT> extends ICstVisitor<IN, OUT> {

src/index.test.ts

@@ -1,6 +1,7 @@
 import { expect, describe, it } from 'vitest'
 
 import { parse } from './index.js'
+import { reservedIdentifiers } from './tokens.js'
 
 describe('specification of CEL', () => {
   describe('comparisons', () => {
@@ -62,4 +63,19 @@ describe('specification of CEL', () => {
       expect(result).toThrow(`Identifier "a" not found in context: {"b":2}`)
     })
   })
+
+  describe('reserved identifiers', () => {
+    it.each(reservedIdentifiers)(
+      'should throw if reserved identifier "%s" is used',
+      (identifier) => {
+        const expr = `${identifier} < 1`
+
+        const result = () => parse(expr)
+
+        expect(result).toThrow(
+          `Detected reserved identifier. This is not allowed`
+        )
+      }
+    )
+  })
 })

src/parser.ts

@@ -11,6 +11,7 @@ import {
   StringLiteral,
   GreaterOrEqualThan,
   LessOrEqualThan,
+  ReservedIdentifiers,
 } from './tokens.js'
 
 export class CelParser extends CstParser {
@@ -65,6 +66,7 @@ export class CelParser extends CstParser {
     this.OR([
       { ALT: () => this.CONSUME(Integer) },
       { ALT: () => this.SUBRULE(this.identifier) },
+      { ALT: () => this.CONSUME(ReservedIdentifiers) },
     ])
   })
 }

src/tokens.ts

@@ -64,13 +64,41 @@ export const Integer = createToken({ name: 'Integer', pattern: /0|[1-9]\d*/ })
 export const Plus = createToken({ name: 'Plus', pattern: /\+/ })
 export const Minus = createToken({ name: 'Minus', pattern: /-/ })
 
+export const reservedIdentifiers = [
+  'as',
+  'break',
+  'const',
+  'continue',
+  'else',
+  'for',
+  'function',
+  'if',
+  'import',
+  'let',
+  'loop',
+  'package',
+  'namespace',
+  'return',
+  'var',
+  'void',
+  'while',
+]
+
+const reserverIdentifiersPattern = reservedIdentifiers.join('|')
+
+export const ReservedIdentifiers = createToken({
+  name: 'ReservedIdentifiers',
+  pattern: new RegExp(reserverIdentifiersPattern),
+})
+
 // The order of tokens is important
 export const allTokens = [
   WhiteSpace,
   OpenParenthesis,
   CloseParenthesis,
   Equals,
-  // keywords must be before Identifier
+  // ReservedIdentifiers must be before Identifiers
+  ReservedIdentifiers,
   Identifier,
   Dot,
   OpenBracket,

src/visitor.ts

@@ -66,6 +66,10 @@ export class CelVisitor
       return this.visit(ctx.identifier)
     }
 
+    if (ctx.ReservedIdentifiers) {
+      throw new Error('Detected reserved identifier. This is not allowed')
+    }
+
     throw new Error('Atomic expression not recognized')
   }